springMVC源码分析--ModelFactory

ModelFactory是用来维护Model的，具体包含两个功能

（1）初始化Model

（2）处理器执行后将Model中相应的参数更新到SessionAttributes中

1、初始化Model其实是对@ModelAttribute和@SessionAttribute注解的执行，执行的操作是在initModel中，包括获取@SessionAttribute注解的参数的值以及被@ModelAttribute注解的函数。

public void initModel(NativeWebRequest request, ModelAndViewContainer mavContainer, HandlerMethod handlerMethod)
			throws Exception {
		//从注解了@SessionAttribute中取出保存的参数，并合并到mavContainer中
		Map<String, ?> sessionAttributes = this.sessionAttributesHandler.retrieveAttributes(request);
		mavContainer.mergeAttributes(sessionAttributes);

		//执行注释了@ModelAttribute的方法并将结果设置到Model
		invokeModelAttributeMethods(request, mavContainer);

		//遍历既注释了@ModelAttribute又在@SessionAttribute注释中的参数
		for (String name : findSessionAttributeArguments(handlerMethod)) {
			if (!mavContainer.containsAttribute(name)) {
				Object value = this.sessionAttributesHandler.retrieveAttribute(request, name);
				if (value == null) {
					throw new HttpSessionRequiredException("Expected session attribute '" + name + "'");
				}
				mavContainer.addAttribute(name, value);
			}
		}
	}

2、更新Model的操作是在updateModel中，首先会更新@SessionAttribute中注解的值，然后会更新Model中的值。

//更新Model，包括两部分一是修改@SessionAttribute注解中值的value，二是更新Model中的值
	public void updateModel(NativeWebRequest request, ModelAndViewContainer mavContainer) throws Exception {
		ModelMap defaultModel = mavContainer.getDefaultModel();
		if (mavContainer.getSessionStatus().isComplete()){
			this.sessionAttributesHandler.cleanupAttributes(request);
		}
		else {
			this.sessionAttributesHandler.storeAttributes(request, defaultModel);
		}
		if (!mavContainer.isRequestHandled() && mavContainer.getModel() == defaultModel) {
			updateBindingResult(request, defaultModel);
		}
	}

ModelFactory的完整源码如下：

public final class ModelFactory {

	private static final Log logger = LogFactory.getLog(ModelFactory.class);

	private final List<ModelMethod> modelMethods = new ArrayList<ModelMethod>();

	private final WebDataBinderFactory dataBinderFactory;

	private final SessionAttributesHandler sessionAttributesHandler;

	public ModelFactory(List<InvocableHandlerMethod> invocableMethods, WebDataBinderFactory dataBinderFactory,
			SessionAttributesHandler sessionAttributesHandler) {

		if (invocableMethods != null) {
			for (InvocableHandlerMethod method : invocableMethods) {
				this.modelMethods.add(new ModelMethod(method));
			}
		}
		this.dataBinderFactory = dataBinderFactory;
		this.sessionAttributesHandler = sessionAttributesHandler;
	}

	public void initModel(NativeWebRequest request, ModelAndViewContainer mavContainer, HandlerMethod handlerMethod)
			throws Exception {
		//从注解了@SessionAttribute中取出保存的参数，并合并到mavContainer中
		Map<String, ?> sessionAttributes = this.sessionAttributesHandler.retrieveAttributes(request);
		mavContainer.mergeAttributes(sessionAttributes);

		//执行注释了@ModelAttribute的方法并将结果设置到Model
		invokeModelAttributeMethods(request, mavContainer);

		//遍历既注释了@ModelAttribute又在@SessionAttribute注释中的参数
		for (String name : findSessionAttributeArguments(handlerMethod)) {
			if (!mavContainer.containsAttribute(name)) {
				Object value = this.sessionAttributesHandler.retrieveAttribute(request, name);
				if (value == null) {
					throw new HttpSessionRequiredException("Expected session attribute '" + name + "'");
				}
				mavContainer.addAttribute(name, value);
			}
		}
	}

	private void invokeModelAttributeMethods(NativeWebRequest request, ModelAndViewContainer mavContainer)
			throws Exception {

		while (!this.modelMethods.isEmpty()) {
			//获取注释了@ModelAttribute的方法
			InvocableHandlerMethod attrMethod = getNextModelMethod(mavContainer).getHandlerMethod();
			//获取注释了@ModelAttribute中设置的value作为参数名
			String modelName = attrMethod.getMethodAnnotation(ModelAttribute.class).value();
			//如果参数名已经在mavContainer中则跳过
			if (mavContainer.containsAttribute(modelName)) {
				continue;
			}

			//执行@ModelAttribute注释的方法
			Object returnValue = attrMethod.invokeForRequest(request, mavContainer);

			if (!attrMethod.isVoid()){
				//使用getNameForReturnValue获取参数名
				String returnValueName = getNameForReturnValue(returnValue, attrMethod.getReturnType());
				if (!mavContainer.containsAttribute(returnValueName)) {
					mavContainer.addAttribute(returnValueName, returnValue);
				}
			}
		}
	}
	//获取每次要处理的ModelMethod
	private ModelMethod getNextModelMethod(ModelAndViewContainer mavContainer) {
		for (ModelMethod modelMethod : this.modelMethods) {
			if (modelMethod.checkDependencies(mavContainer)) {
				if (logger.isTraceEnabled()) {
					logger.trace("Selected @ModelAttribute method " + modelMethod);
				}
				this.modelMethods.remove(modelMethod);
				return modelMethod;
			}
		}
		ModelMethod modelMethod = this.modelMethods.get(0);
		if (logger.isTraceEnabled()) {
			logger.trace("Selected @ModelAttribute method (not present: " +
					modelMethod.getUnresolvedDependencies(mavContainer)+ ") " + modelMethod);
		}
		this.modelMethods.remove(modelMethod);
		return modelMethod;
	}
	//查找被@SessionAttribute注解的并且被@ModelAttribute注解的参数
	private List<String> findSessionAttributeArguments(HandlerMethod handlerMethod) {
		List<String> result = new ArrayList<String>();
		for (MethodParameter parameter : handlerMethod.getMethodParameters()) {
			if (parameter.hasParameterAnnotation(ModelAttribute.class)) {
				String name = getNameForParameter(parameter);
				//判断是否@SessionAttribute注解中的值
				if (this.sessionAttributesHandler.isHandlerSessionAttribute(name, parameter.getParameterType())) {
					result.add(name);
				}
			}
		}
		return result;
	}
	//获取参数名称
	public static String getNameForParameter(MethodParameter parameter) {
		ModelAttribute annot = parameter.getParameterAnnotation(ModelAttribute.class);
		String attrName = (annot != null) ? annot.value() : null;
		return StringUtils.hasText(attrName) ? attrName :  Conventions.getVariableNameForParameter(parameter);
	}
	//获取@ModelAttribute注解中的值
	public static String getNameForReturnValue(Object returnValue, MethodParameter returnType) {
		ModelAttribute annotation = returnType.getMethodAnnotation(ModelAttribute.class);
		if (annotation != null && StringUtils.hasText(annotation.value())) {
			return annotation.value();
		}
		else {
			Method method = returnType.getMethod();
			Class<?> resolvedType = GenericTypeResolver.resolveReturnType(method, returnType.getContainingClass());
			return Conventions.getVariableNameForReturnType(method, resolvedType, returnValue);
		}
	}
	//更新Model，包括两部分一是修改@SessionAttribute注解中值的value，二是更新Model中的值
	public void updateModel(NativeWebRequest request, ModelAndViewContainer mavContainer) throws Exception {
		ModelMap defaultModel = mavContainer.getDefaultModel();
		if (mavContainer.getSessionStatus().isComplete()){
			this.sessionAttributesHandler.cleanupAttributes(request);
		}
		else {
			this.sessionAttributesHandler.storeAttributes(request, defaultModel);
		}
		if (!mavContainer.isRequestHandled() && mavContainer.getModel() == defaultModel) {
			updateBindingResult(request, defaultModel);
		}
	}
	//
	private void updateBindingResult(NativeWebRequest request, ModelMap model) throws Exception {
		List<String> keyNames = new ArrayList<String>(model.keySet());
		for (String name : keyNames) {
			Object value = model.get(name);

			if (isBindingCandidate(name, value)) {
				String bindingResultKey = BindingResult.MODEL_KEY_PREFIX + name;

				if (!model.containsAttribute(bindingResultKey)) {
					WebDataBinder dataBinder = dataBinderFactory.createBinder(request, value, name);
					model.put(bindingResultKey, dataBinder.getBindingResult());
				}
			}
		}
	}
	//
	private boolean isBindingCandidate(String attributeName, Object value) {
		if (attributeName.startsWith(BindingResult.MODEL_KEY_PREFIX)) {
			return false;
		}

		Class<?> attrType = (value != null) ? value.getClass() : null;
		if (this.sessionAttributesHandler.isHandlerSessionAttribute(attributeName, attrType)) {
			return true;
		}

		return (value != null && !value.getClass().isArray() && !(value instanceof Collection) &&
				!(value instanceof Map) && !BeanUtils.isSimpleValueType(value.getClass()));
	}

	private static class ModelMethod {

		private final InvocableHandlerMethod handlerMethod;

		private final Set<String> dependencies = new HashSet<String>();

		private ModelMethod(InvocableHandlerMethod handlerMethod) {
			this.handlerMethod = handlerMethod;
			for (MethodParameter parameter : handlerMethod.getMethodParameters()) {
				if (parameter.hasParameterAnnotation(ModelAttribute.class)) {
					this.dependencies.add(getNameForParameter(parameter));
				}
			}
		}

		public InvocableHandlerMethod getHandlerMethod() {
			return this.handlerMethod;
		}

		public boolean checkDependencies(ModelAndViewContainer mavContainer) {
			for (String name : this.dependencies) {
				if (!mavContainer.containsAttribute(name)) {
					return false;
				}
			}
			return true;
		}

		public List<String> getUnresolvedDependencies(ModelAndViewContainer mavContainer) {
			List<String> result = new ArrayList<String>(this.dependencies.size());
			for (String name : this.dependencies) {
				if (!mavContainer.containsAttribute(name)) {
					result.add(name);
				}
			}
			return result;
		}

		@Override
		public String toString() {
			return this.handlerMethod.getMethod().toGenericString();
		}
	}

}